Process and apparatus for controlling the spacing of the electrodes of electrolytic cells

ABSTRACT

Process and apparatus for controlling the spacing of the anodes with respect to the cathode in an electrolytic cell including a positioning arrangement for moving the anodes up and down in response to a control signal and means for generating the control signal by comparing the field generated by the bus bars carrying current to the anodes with the individual fields generated by field coils to which a current proportional to the total electrolysis current is supplied. A reed switch is responsive to the opposing fields and serves to actuate the positioning arrangement when a threshold in the resulting fields is detected.

Oct. 2, 1973 3,689,398 9/1972 Caleffi 204/228 X PROCESS AND APPARATUS FOR CONTROLLING THE SPACING OF THE ELECTRODES or ELECTROLYTIC CELLS FOREIGN PATENTS OR APPLICATIQNS Inventors:

4. 4 1968 204 2 [75] Fitz Engelmann, Ranzel; Johannes 8 Great Bmam 25 Knoch, Mondorf; Christoph Viehweger, Ranzel, all of Germany Primary Examiner lohn H. Mack Dynamit Nobel Aktiengesellschaft,

Assistant Examiner-D. R. Valentine Att0rneyCraig, Antonelli and Hill [22] Filed: Nov. 1, 1971 ABSTRACT 21 Appl. No.: 194,309

Process and apparatus for controlling the spacing of the anodes with respect to the cathode in an electrolytic cell including a positioning arrangement for moving the [30] Foreign Application Priority Data Oct. 31, 1970 Germany......,............

anodes up and down in response to a control signal and i means for generating the control signal by comparing U.S. 204/1 R, 204/99, 204/219, the field generated y the bus bars y g current to 204/225 B0lk 1/00, COld l/14, BOlk 3/00 Field of Search........................

the anodes with the individual fields generated by field coils to which a current proportional to the total electrolysis current is supplied. A reed switch is responsive m l C L n I ll. oo 55 to the opposing fields and serves to actuate the positioning arrangement when a threshold in the resulting fields is detected.

[ 56] References Cited UNITED STATES PATENTS 3,594,300 7/1971 Schafer......................Q.... 204/228 X 10 Claims, 1 Drawing Figure PROCESS AND APPARATUS FOR CONTROLLING THE SPACING OF THE ELECTRODES OF ELECTROLYTIC CELLS This invention relates to a process and apparatus for controlling the distance between the anodes and the cathode in electrolytic cells for the electrolysis of aequeous solutions, wherein the anodes are adjusted by means of an adjusting mechanism driven by an electric motor, of the type described in U.S. Pat. No. 3,574,073.

Electrolytic cells of the type to which the present invention is applicable may consist, for example, of a covered elongated trough slightly inclined toward one end thereof. The cathode is provided in the form of a fluid mercury layer introduced at the elevated end of the cell and flowing along the bottom of the cell toward the lowered end thereof. The plural anodes consist, for example, of rectangular blocks made of graphic or metal, for instance, which are suspended from conductive lead-in lines. The undersides of the anodes are disposed at a minor spacing above the flowing mercury cathode.

In cells of this type, the accurate spacing between the graphic anodes and the mercury cathode is of extraordinary importance. This spacing between the electrodes must be as small as possible in order to exclude to the greatest extent possible the useless consumption of energy, for example in the generation of heat. Also, undesirable secondary reactions occur if this distance becomes too small.

During operation of the cell, the graphite anodes are consumed, so that the distance between the anodes and the cathode increases, resulting in an impaired power economy. In addition, the graphite consumption of the anodes disposed more closely to the inlet end of the cell is lower than that at the outlet end of the cell. Thus, in order to maintain the correct spacing between the anodes and the cathode, the elevation of the anodes must be adjusted from time to time.

Additional difficulties are encountered in the operation of such mercury cells with graphite anodes in case short circuits occur. Such short circuits can be caused, for example, by a breaking of the graphite electrode, by a loosening of the anode supports, by a change in the thickness of the mercury layer due to inclusions of thick mercury (viscid mercury) or faulty flow control, or other reasons, because of which the graphite anode comes into contact with the flowing mercury cathode. The thus-produced short circuit generates an excessively strong current flow in the anode, in the bus bar supplying this anode, etc.

In many conventional devices for adjusting the distance between the electrodes, each anode must be adjusted individually, in part by hand. Also, an apparatus and a process are disclosed in the above-referenced U.S. patent wherein the anodes of 'an electrolytic cell are moved in groups via a mechanical shifting device, wherein a hydraulic control is produced electrically by way of a solenoid-operated switch attached to the bus bar leading to the anode; this switch responds to the change in the flux of the magnetic field of the bus bar. This device concerns a solenoid-operated switch operating under a protective gas atmosphere and adjustably mounted on the bus bar. If a direct current flows through the bus bar, a magnetic field is formed around this bus bar. This magnetic field is weakest in the direction of the current, i.e., in the longitudinal extension of the bus bar. The field increases toward the transverse direction with respect to the bus bar and is strongest at i.e., at right angles to the bus bar. When introducing a correspondingly designed solenoid-operated switch into this magnetic field, the switch closes its contact, during rotation from 0 to 90 at some point within the 90 range. If percent electrolytic current corresponds to this position, i.e.,,for example, the closing point, the thusset solenoid-operated switch will close its contact when this overcurrent occurs and thus serves as the command-giving control means for elevating the anode or group of anodes by means of the appropriate adjusting mechanism.

In order to improve the sensitivity of response, this conventional solenoid-operated switch is surrounded by a small iron tube, whereby it is magnetically shielded, for example, up to about 80 percent of the operating value and the magnetic field in the iron tube becomes effective with respect to the solenoid-operated switch only when this value has been exceeded. The essential disadvantage of this device resides in the fact that, due to the fixedly set position of the solenoidoperated switch on the bus bar, only one operating point per switch is provided; for example, protection is afforded only at 30 percent overcurrent. This disadvantage can be overcome only by the arrangement of several switches on the same bus bar, in order to obtain different response values. However, this is very complicated and expensive. Otherwise, the set solenoidoperated switches would have to be adjusted, in each case, to a new response value, which, in turn, would consume considerable amounts of time and money. The repeated adjustment procedure becomes particularly difficult for an electrolysis process operating at varying load.

It is the object of this invention to eliminate the dis advantages inherent in conventional processes and apparatus in the adjustment of the electrode spacing during operation.

According to the invention, it is suggested that the signal for giving the command fo adjusting the spacing be obtained from the difference between the magnetic field generated by the current of the bus bar corresponding to an anode group and the magnetic field which is generated at each bus bar in a field coil through which passes an energizing current equivalent to the electrolytic current and which counteracts the magnetic field of the bus bar. It has now been made possible, by this invention, to obtain difierent response thresholds for the signal generation for partial load and alternating load of the electrolytic current, with only a single switching device per bus bar.

This infinite, load-dependent control of the response threshold for the signal is attained, according to a further feature of this invention, by means effecting a correspondng variation and/or adjustment of the energizing current for the magnet coils. According to the invention, the contacts of a solenoid-operated switch, disposed within the field coil, are closed by a change in the difference of the magnetic fields of the bus bar and the field coil because of a higher current load on the bus bar.

Thus, the process and apparatus according to the present invention for controlling; the distance between the electrodes of an electrolytic system to protect the same against current overloads and short circuits are essentially distinguished by the incorporation of a solenoid-operated switch into a correspondingly wound and dimensioned field coil on each bus bar leading to an anode, which coil has an induction current flowing therethrough which is controllable and is equivalent to the electrolytic current, this coil counteracting the magnetic field of the bus bar. By regulating this energizing current via, for example, only one control element for an entire electrolysis system, a loaddependent response threshold can be set with only one switching mechanism per bus bar.

For an electrolysis operation, a large number of elec trolytic cells are normally required, which cells operate in parallel. in each electrolytic cell, in turn, a large number of anodes are disposed side-by-side. When applying the process and the associated apparatus of this invention to an entire electrolysis arrangement, a switching device consisting of a solenoid-operated switch and a field coil is required for each bus bar leading to an anode. For purposes of simplification, and also economic considerations, the anodes of one electrolytic cell are combined into groups, preferably two groups, and adjusted as a group. In a further development of the invention one control mechanism with one respective electric motor are provided per anode group of one electrolytic cell, in order to adjust this anode group. Of course, in addition to this automatic adjustment of the anodes according to the invention, a manually operable adjustment possibility is also additionally provided for each anode or anode group.

The operation of the electrolytic cells becomes more economical by the process and the associated apparatus of this invention, since the automatic adjustment and control of the electrode spacing, via the shifting of the anodes, protects the system from current overloads and short circuits, because the automatic adjustment in each case ensures the lowest voltage loss. Besides, the invention exhibits the advantage that it can be utilized any time during partial load or varying load of the electrolysis system.

Additional details of the invention are illustrated in the Drawing, which consists of a schematic circuit diagram of one embodiment, and will be explained in greater detail hereinbelow with reference thereto.

In the Drawing, a schematic circuit diagram is shown, in principle, of a system for the lifting and lowering of the anodes of an electrolytic cell, wherein the electrolytic cell contains fourteen anodes, for example of graphite, combined into two groups of seven anodes each, which anodes are in each instance adjusted together as a group. The solenoid-operated switches 121 through 127 or 221 through 227, disposed with the field coils 111 117 and 211 217, respectively, are associated with the bus bars 101 107 and 201 207, respectively, leading to the anodes. The contacts of the solenoid-operated switches consist of a ferromagnetic material, and so, under the effect of a magnetic field, the contacts are attracted to each other and thus establish an electrical connection. The contacts are disposed, in this arrangement, within the field coils 111 117 and 211 217 which latter have current flowing therethrough which is proportional to the electrolysis current so that the field thereof will oppose the magnetic field of the anode bus bars 101 107 and 201 207 at the solenoid-operated switch and thus vary the 217 with the contacts at an angle of, for example, 20 30 with respect to the current direction of the bus bars.

The field coils are connected to a controllable current source, wherein a supply voltage is filtered by filter arrangement 4 and applied to the primary side of the transformer 3. From this transformer 3 a supply voltage of 12 volts is derived for the control mechanism and is rectified by the converter 5. The control voltage is of such a value that the functional clement exhibits a binary signal l if its potential with respect to the negative pole M is larger than 7V. The output of the func tional element has a binary 0" signal if its potential with respect to the negative pole M is smaller than 1V.

in addition, the supply voltage is applied from the transformer 3 to a proportional amplifier 1 via the symmetry-monitoring element 2; in this way, the input control for the field coils 111 117 or 211 217 can be varied via the leads 6 to this converter in order to change the response thresholds. Preferably, the response threshold values are controlled in such a manner that a signal emission takes place in any event at approximately 1.3 of the total current in a bus bar divided by the number of bus bars forming an electrolytic cell.

From the contacts of the solenoid-operated switches 121 127 and 221 227, respectively, the lines 131 137 and 231 237, respectively, carrying the signal voltage, lead to the control units for the electric motors 14 and 24, connected thereto, for the lifting and lowering of the anodes. Upon an increase of the current in one of the bus bars 101-107 and 201-207, respectively, up to the set response threshold value of the solenoid-operated switches, for example to 130 percent of the rated current, the contact of the respective solenoid-operated switch is closed and passes the signal voltage via the OR gates 10 or 20, depending on which anode group was subjected to the overcurrent, to the time-base member or flip-flop 11 or 21, which can optionally operate with a delay. The flip-flop energizes the ignition pulse generator 12 or 22, which latter operates via the thyristor set 13 or 23 to energize the motor 14 or 24, respectively, for lifting the anodes of the respective half of the cell by controlling the three phase supply voltage of the motor in the conventional manner. Once the rated current is again reached during the elevation of the anodes and the break value of the respectively energized contact is surpassed, for example at about percent of the response threshold value, the signal disappears again, and the motor 14 or 24 is switched off.

From the timing element 15 or 25, respectively, after a predetermined delay time, a short-term signal is now applied via the flip-flop 16 or 26 to the signal storage means 17 or 27, respectively. This short-term signal can switch over the signal storage means only when the make-ready input 18 or 28 likewise receives a signal. This signal is present only when the final-position signaling means 19 or 29 is not excited, i.e., when the anodes are not in the operating position, in other words when they are lifted. The output signal of the signal storage means 17 or 27 controls, via the OR gate 30 or 40, the ignition pulse generator 31 or 41, the latter switching on the motor 14 or 24 for the downward movement via the thyristor set 13 or 23, respectively. The downward movement is limited in the downward direction by the final position indicator 19 or 29.

If, during the upward movement,-after a predetermined period of time, for example 2 minutes, the rated current has not been attained, the upward movement is terminated via the timer member 32 or 42, and the pulse for inserting the bridging switch 9 for the entire cell is emitted from the timer member.

Besides, an indication of the control procedure is transmitted via the signal storage means 8 to the control station. Furthermore, the number of the anode which has triggered the procedure appears at the digital tube 33 or 43, respectively. An audible indicator of the control operation may also be provided. During normal operation, the digit indicates that the control mecha nism is ready for the monitoring process.

In addition to the automatic adjustment, the lifting and lowering of the anodes of a half of a cell can be effected by hand with the associated operating elements, which, however, is not illustrated herein.

As can be readily seen from the foregoing description, the control over the operating threshold of the anode adjusting system is based on the value of the electrolysis current. The electrolysis current is adjusted to a nominal value by regulating means (not shown) and the exciting current supplied to the magnetic coils is regulated by the proportional amplifier 1 to be directly proportional to the total electrolysis current. Therefore, the electrolysis current, and also the current supplied to the coils, can be assumed to remain constant at any adjusted load rating for the purposes of this invention.

The magnetic switches associated with each bus prevent the current from exceeding a certain maximum value in the various buses, the maximum value being dependent on the given load being carried. The mag netic field of the various coils is constant for whatever load it is adjusted since it is based on the average electrolysis current, and so the field generated by the various buses, which in practice will vary due to unavoidable fluctuations of the current, will be easily detected. If the current rises in one bus bar so high that the difference in the two magnetic fields is sufficient to close the associated reed switch, then the anode group is moved up and thereby the current is lowered again to the permissible value.

What we claim is:

1. Process for controlling the spacing between at least one anode and a cathode in an electrolytic cell wherein the anode connected to a voltage source via a bus bar is adjusted by means of an adjusting mechanism driven by an electric motor, comprising generating a control signal representing the difference between the magnetic field generated by the current of the bus bar connected to the anode and a magnetic field which is generated'at each bus bar in a field coil through which passes an energizing current equivalent to the electrolytic current and which counteracts the magnetic field of the bus bar, detecting the level of said control signal, and operating said adjusting mechanism upon detection of the level of said control signal exceeding a prescribed level.

2. Process according to claim 1, further comprising the step of adjusting the magnitude of the equivalent current passing through said field coil.

3. Apparatus for controlling the spacing between at least one anode and a cathode in an electrolytic cell having a bus bar supplying current to said anode comprising adjusting means for adjusting the position of said anode with respect to said cathode, controllable switching means associated with said bus bar supplying current to said anode for controlling the application of operating current to said adjusting means, including a field coil receiving an energizing current equivalent to the electrolytic current and generating a field which counteracts the magnetic field of the bus bar to produce a composite field and a switching unit responsive to a prescribed value of the composite field for selectively connecting said adjusting means to a source of operating current.

4. Apparatus according to claim 3, including control means for providing energizing current for the excitation of said field coil.

5. Apparatus according to claim 4, characterized in that the field coil and the switch unit is arranged on the bus bar at an angle of 20 to 30 with respect to the direction of the current flow in the bus bar.

6. Apparatus according to claim 5, wherein a plural' ity of anodes are provided in association with said cathode, said switching means including a switching unit for each anode, the switching units of the anodes of one electrolytic cell being connected in two groups to one control means for said adjusting means.

7. Apparatus according to claim 6, wherein said control means includes an OR gate having an input connected to each switching unit and an output connected to an ignition pulse generator providing control pulses to a thyristor set, said thyristor set being connected be tween a source of energizing voltage and said adjusting means.

8. Apparatus according to claim 7, further comprising a timing element cnnected to a flip-flop serving as a signal storage means, the second input of which is connected to a final position indicator for indicating the operating position of the anodes, the output of said flip-flop being connected via a second OR gate to said ignition pulse generator.

9. Apparatus according to claim 8, wherein a second timing element is provided between output of said OR gate and said ignition pulse generator, which timing element is also connected to a bridging switch for the entire electrolytic cell.

10. Apparatus according to claim 9, characterized in that the switching units are connected to an optical indicating means for indicating the switching unit which has been actuated. 

2. Process according to claim 1, further comprising the step of adjusting the magnitude of the equivalent current passing through said field coil.
 3. Apparatus for controlling the spacing between at least one anode and a cathode in an electrolytic cell having a bus bar supplying current to said anode comprising adjusting means for adjusting the position of said anode with respect to said cathode, controllable switching means associated with said bus bar supplying current to said anode for controlling the application of operating current to said adjusting means, including a field coil receiving an energizing current equivalent to the electrolytic current and generating a field which counteracts the magnetic field of the bus bar to produce a composite field and a switching unit responsive to a prescribed value of the composite field for selectively connecting said adjusting means to a source of operating current.
 4. Apparatus according to claim 3, including control means for providing energizing current for the excitation of said field coil.
 5. Apparatus according to claim 4, characterized in that the field coil and the switch unit is arranged on the bus bar at an angle of 20* to 30* with respect to the direction of the current flow in the bus bar.
 6. Apparatus according to claim 5, wherein a plurality of anodes are provided in association with said cathode, said switching means including a switching unit for each anode, the switching units of the anodes of one electrolytic cell being connected in two groups to one control means for said adjusting means.
 7. Apparatus acCording to claim 6, wherein said control means includes an OR gate having an input connected to each switching unit and an output connected to an ignition pulse generator providing control pulses to a thyristor set, said thyristor set being connected between a source of energizing voltage and said adjusting means.
 8. Apparatus according to claim 7, further comprising a timing element cnnected to a flip-flop serving as a signal storage means, the second input of which is connected to a final position indicator for indicating the operating position of the anodes, the output of said flip-flop being connected via a second OR gate to said ignition pulse generator.
 9. Apparatus according to claim 8, wherein a second timing element is provided between output of said OR gate and said ignition pulse generator, which timing element is also connected to a bridging switch for the entire electrolytic cell.
 10. Apparatus according to claim 9, characterized in that the switching units are connected to an optical indicating means for indicating the switching unit which has been actuated. 